Update CHANGELOG

Author: kngwyu

CHANGELOG.md

@@ -4,6 +4,9 @@ Change Log
 All notable changes to this project will be documented in this file. This
 project adheres to [Semantic Versioning](http://semver.org/).
 
+# 2.1.27
+- Update the version of rustc-ap-syntax
+
 # 2.1.26
 - Update the version of rustc-ap-syntax